Flat heat generator for generating heat through an electric action are widely used in a variety of fields.
For example, a flat heat generator may be adhered to a mechanical device in order to maintain the same at a constant temperature, or a flat heat generator may be adhered around a liquid container when a liquid within the container needs to be prevented from freezing, or when the liquid needs temperature adjustments such as heat insulation, heating and the like. Similarly, a flat heat generator may be employed for a liquid carrier pipe which requires heat insulation by wrapping the flat heat generator around the pipe to prevent a liquid passing therethrough from cooling down. Also, a flat heat generator may be used as an underfloor heating sheet for residences. Further, a liquified gas for use in an industrial liquified gas supply station could be suddenly released to cause the temperature of the pipe to abruptly fall down. Depending on the type of the gaseous fluid, it can be crystallized to block the passage. Such a liquified gas supply station prevents the gaseous fluid from crystallization and deposition by heating the gaseous fluid with an electric wire heater or the like. Specifically, a variety of gas flow controllers including a pressure adjuster, a filter, a pressure sensor, a flow meter, and the like, which comprise such a liquified gas supply station, are covered with and heated by laminar flat heat generators, thereby preventing crystallization within the pipe.
A carbon fiber sheet is known to generate heat with electric power in accordance with its resistance, due to the fact that carbon is a conductor, when an electric potential is applied across electrodes attached to the carbon fiber sheet to cause a current to flow between the electrodes. In the past, when a carbon fiber sheet is employed as a flat heat generator for generating heat through an electric action, electrodes made of copper foil tape or silver paste are adhered to the carbon fiber sheet. Then, a heat-resistant agglutinant polyethylene film or agglutinant polyimide film is pressed over the carbon fiber sheet with a high-temperature, high-pressure press to form an insulating protective film. In this way, the flat heat generator is manufactured. Then, parts of the electrodes thus attached to the carbon fiber sheet are peeled off, and the peeled electrodes are used as power supply terminals.
FIG. 1 shows a top plan view of a conventional flat heat generator which employs a rectangular carbon fiber sheet 1 which comprises an electrode 2 made of a copper foil tape, a cross-sectional view of the flat heat generator, and a partially enlarged cross-sectional view of the flat heat generator. The carbon fiber sheet 1 is covered with an insulating protective film 3.
According to such a conventional flat heat generator, since the electrode can be merely adhered to the surface of the carbon fiber sheet, a large contact resistance is present between the electrode and the carbon fiber sheet, which can arise the following problems: a lower powering efficiency resulting from variations in contact resistance, heating due to a contact failure, and the like. Moreover, since the copper tape and silver paste for the electrode can be applied only at extremities of the carbon fiber sheet, the electrode cannot but being limited in shape.